There are two very general sets of providers: the ones who care about creating a repeat client base and a good reputation, and the ones who treat a client like a number and don't care about their rep.
The latter "cash and dash" types are YMMV in the worst way, and research will reveal that tendency.
The former generally base YMMV on two main issues: the client's hygiene and/or attitude. The better both are, the higher the potential is for good chemistry... and this has less to do with youth or handsomeness than one might imagine. Be nice, be super-clean, have reasonable expectations.